Fan variable area nozzle with cable actuator system

ABSTRACT

A fan variable area nozzle (FVAN) includes a flap driven through a cable which circumscribes the fan nacelle. The cable is strung through a multiple of flaps to define a flap set of each circumferential sector of the EVAN. An actuator system includes a compact high power density electromechanical actuator which rotates a spool to deploy and retract the cable and effectively increase or decrease the length thereof between the spool and a fixed attachment to increase and decrease the fan nozzle exit area.

BACKGROUND OF THE INVENTION

The present invention relates to a gas turbine engine, and more particularly to a turbofan gas turbine engine having a cable driven fan variable area nozzle structure within the fan nacelle thereof.

Conventional gas turbine engines include a fan section and a core engine with the fan section having a larger outer diameter than that of the core engine. The fan section and the core engine are disposed sequentially about a longitudinal axis and are enclosed in a nacelle. An annular path of primary airflow passes through the fan section and the core engine to generate primary thrust.

Combustion gases are discharged from the core engine through a primary airflow path and are exhausted through a core exhaust nozzle. An annular fan flow path, disposed radially outwardly of the primary airflow path, passes through a radial outer portion between a fan nacelle and a core nacelle and is discharged through an annular fan exhaust nozzle defined at least partially by the fan nacelle and the core nacelle to generate fan thrust. A majority of propulsion thrust is provided by the pressurized fan air discharged through the fan exhaust nozzle, the remaining thrust provided from the combustion gases is discharged through the core exhaust nozzle.

The fan nozzles of conventional gas turbine engines have fixed geometry. The fixed geometry fan nozzles are suitable for take-off and landing conditions as well as for cruise conditions. However, the requirements for take-off and landing conditions are different from requirements for the cruise condition. Optimum performance of the engine may be achieved during different flight conditions of an aircraft by varying the fan exhaust nozzle for the specific flight regimes.

Some gas turbine engines have implemented fan variable area nozzles. The fan variable area nozzle provide a smaller fan exit nozzle diameter during cruise conditions and a larger fan exit nozzle diameter during take-off and landing conditions. The existing variable area nozzles typically utilize relatively complex mechanisms that increase engine weight to the extent that the increased fuel efficiency benefits gained from fan variable area nozzle are negated.

Accordingly, it is desirable to provide an effective, lightweight fan variable area nozzle for a gas turbine engine.

SUMMARY OF THE INVENTION

A fan variable area nozzle (FVAN) according to the present invention includes a flap assembly which defines the fan nozzle exit area. The flaps are incorporated into the fan nacelle to define a trailing edge thereof. The flap assembly generally includes a multiple of flaps driven through a cable which circumscribes the fan nacelle. The cable engages each flap at a flap engagement point and a multiple of fixed fan nacelle structures at a fixed engagement point such as a fan nacelle rib.

The cable is strung through a multiple of flaps to define a flap set within each of a multiple of circumferential FVAN sectors. That is, a separate cable is utilized within each circumferential sector such that each cable can be individually driven by an actuator within the actuator system.

The actuator system engages an end segment of the cable such that the cable may be spooled and unspooled to effectively increase or decrease the cable length between a spool and a fixed attachment to increase and decrease the fan nozzle exit area. The bypass flow permits unilateral operation of the FVAN such that the bypass flow operates to diverge the flaps. This results in a significant weight savings and uncomplicated operation.

The present invention therefore provides an effective, lightweight fan variable area nozzle for a gas turbine engine.

BRIEF DESCRIPTION OF THE DRAWINGS

The various features and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the currently preferred embodiment. The drawings that accompany the detailed description can be briefly described as follows:

FIG. 1A is a general perspective view an exemplary turbo fan engine embodiment for use with the present invention;

FIG. 1B is a perspective partial fragmentary view of the engine;

FIG. 1C is a rear view of the engine;

FIG. 2A is a perspective partial phantom view of a section of the FVAN; and

FIG. 2B is an expanded view of one flap assembly of the FVAN.

FIG. 2C is a partial phantom view of a section of the FVAN.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1A illustrates a general partial fragmentary schematic view of a gas turbofan engine 10 suspended from an engine pylon P within an engine nacelle assembly N as is typical of an aircraft designed for subsonic operation.

The turbofan engine 10 includes a core engine within a core nacelle 12 that houses a low spool 14 and high spool 24. The low spool 14 includes a low pressure compressor 16 and low pressure turbine 18. The low spool 14 drives a fan section 20 connected to the low spool 14 through a gear train 22. The high spool 24 includes a high pressure compressor 26 and high pressure turbine 28. A combustor 30 is arranged between the high pressure compressor 26 and high pressure turbine 28. The low and high spools 14, 24 rotate about an engine axis of rotation A.

The engine 10 is preferably a high-bypass geared turbofan aircraft engine. Preferably, the engine 10 bypass ratio is greater than ten (10), the fan diameter is significantly larger than that of the low pressure compressor 16, and the low pressure turbine 18 has a pressure ratio that is greater than 5. The gear train 22 is preferably an epicyclic gear train such as a planetary gear system or other gear system with a gear reduction ratio of greater than 2.5. It should be understood, however, that the above parameters are only exemplary of a preferred geared turbofan engine and that the present invention is likewise applicable to other gas turbine engines.

Airflow enters a fan nacelle 34 which at least partially surrounds the core nacelle 12. The fan section 20 communicates airflow into the core nacelle 12 to power the low pressure compressor 16 and the high pressure compressor 26. Core airflow compressed by the low pressure compressor 16 and the high pressure compressor 26 is mixed with the fuel in the combustor 30 where is ignited, and burned. The resultant high pressure combustor products are expanded through the high pressure turbine 28 and low pressure turbine 18. The turbines 28, 18 are rotationally coupled to the compressors 26, 16 respectively to drive the compressors 26, 16 in response to the expansion of the combustor product. The low pressure turbine 18 also drives the fan section 20 through the gear train 22. A core engine exhaust E exits the core nacelle 12 through a core nozzle 43 defined between the core nacelle 12 and a tail cone 32.

The core nacelle 12 is supported within the fan nacelle 34 by structure 36 often generically referred to as an upper and lower bifurcation. A bypass flow path 40 is defined between the core nacelle 12 and the fan nacelle 34. The engine 10 generates a high bypass flow arrangement with a bypass ratio in which over 80 percent of the airflow entering the fan nacelle 34 becomes bypass flow B. The bypass flow B communicates through the generally annular bypass flow path 40 and is discharged from the engine 10 through a fan variable area nozzle (FVAN) 42 (also illustrated in FIG. 1B) which varies an effective fan nozzle exit area 44 between the fan nacelle 34 and the core nacelle 12.

Thrust is a function of density, velocity, and area. One or more of these parameters can be manipulated to vary the amount and direction of thrust provided by the bypass flow B. The FVAN 42 changes the physical area and geometry to manipulate the thrust provided by the bypass flow B. However, it should be understood that the fan nozzle exit area 44 may be effectively altered by methods other than structural changes. Furthermore, it should be understood that effectively altering the fan nozzle exit area 44 need not be limited to physical locations approximate the end of the fan nacelle 34, but rather, may include the alteration of the bypass flow B at other locations.

The FVAN 42 defines the fan nozzle exit area 44 for discharging axially the fan bypass flow B pressurized by the upstream fan section 20 of the turbofan engine. A significant amount of thrust is provided by the bypass flow B due to the high bypass ratio. The fan section 20 of the engine 10 is preferably designed for a particular flight condition—typically cruise at 0.8 M and 35,000 feet. The fan section 20 includes fan blades which are designed at a particular fixed stagger angle for an efficient cruise condition. The FVAN 42 is operated to vary the fan nozzle exit area 44 to adjust fan bypass air flow such that the angle of attack or incidence on the fan blades are maintained close to design incidence at other flight conditions such as landing and takeoff, thus enabling optimized engine operation over a range of flight condition with respect to performance and other operational parameters such as noise levels. Preferably, the FVAN 42 defines a nominal converged position for the fan nozzle exit area 44 at cruise and climb conditions, but radially opens relative thereto to define a diverged position for other flight conditions. The FVAN 42 preferably provides an approximately 20% (twenty percent) change in the fan nozzle exit area 44. It should be understood that other arrangements as well as essentially infinite intermediate positions as well as thrust vectored positions in which some circumferential sectors of the FVAN 42 are converged relative to other diverged circumferential sectors are likewise usable with the present invention.

The FVAN 42 is preferably separated into at least four sectors 42A-42D (FIG. 1C) which are each independently adjustable to asymmetrically vary the fan nozzle exit area 44 to generate vectored thrust. It should be understood that although four sectors are illustrated, any number of sectors may alternatively be provided.

In operation, the FVAN 42 communicates with a controller C or the like to adjust the fan nozzle exit area 44 in a symmetrical and asymmetrical manner. Other control systems including an engine controller or aircraft flight control system may also be usable with the present invention. By adjusting the entire periphery of the FVAN 42 symmetrically in which all sectors are moved uniformly, thrust efficiency and fuel economy are maximized during each flight condition. By separately adjusting the circumferential sectors 42A-42D of the FVAN 42 to provide an asymmetrical fan nozzle exit area 44, engine bypass flow is selectively vectored to provide, for example only, trim balance, thrust-controlled maneuvering, enhanced ground operations and short field performance.

Referring to FIG. 2A, the FVAN 42 generally includes a flap assembly 48 which define the fan nozzle exit area 44. The flaps 48 are preferably incorporated into the end segment 34S of the fan nacelle 34 to define a trailing edge 34T thereof. The flap assembly 48 generally includes a multiple of flaps 50, each with a respective linkage system 52 and an actuator system 54.

Each flap 50 defines a pitch point 56 about which the flap 50 pivots relative the fan nacelle 34 (best illustrated in FIG. 2B). Forward of the pitch point 56 relative the trailing edge 34T, the linkage system 52 preferably engages the flap 50. It should be understood that other locations may likewise be usable with the present invention.

The linkage system 52 preferably includes a cable 58 which circumscribes the fan nacelle 34. The cable 58 engages each flap 50 at a flap engagement point 60 and a multiple of fixed fan nacelle structures 34R such as fan nacelle ribs or such like at a fixed engagement point 62. The flap engagement point 60 is preferably located within a flap extension 64 (FIG. 2B) which extends forward of the pivot point 56 relative the trailing edge 34T and is preferably contained within the fan nacelle 34. It should be understood that various flap extensions 64 and the like may be utilized within the flap linkage 52 to receive the cable 58 and that only a simplified kinematics representation is illustrated in the disclosed embodiment.

The cable 58 is preferably strung within the fan nacelle 34 to pass through one fixed engagement point 62, the flap engagement point 60 and a second fixed engagement point 62 (FIG. 2C). That is, the flap engagement point 60 is intermediate the fixed engagement points 62. The fixed engagement point 62 and the flap engagement point 60 are generally eyelets or like which permit the cable to be strung therethrough. The eyelets may include roller, bushing, or bearing structures which minimizes friction applied to the cable 58 at each point 60, 62. Preferably, the cable 58 is strung through a multiple of flaps 50 to define a flap set of each circumferential sectors 42A-42D of the FVAN 42. That is, a separate cable 58 is utilized within each circumferential sector 42A-42D such that each cable 58 is individually driven by the actuator system 54 to asymmetrically adjust the FVAN 42.

Preferably, the actuator system includes a compact high power density electromechanical actuator (EMA) 65 or a rotary hydraulic actuator which rotates a spool 66 connected thereto. Alternatively, a linear actuator may be also utilized to directly pull the cable 58 to change the effective length thereof. That is, the cable 58 is pulled transverse to the length thereof such that the overall length is essentially “spooled” and “unspooled.” It should be understood that a cable-driven system inherently facilitates location of the actuator 65 relatively remotely from the multiple of flaps 50 through various pulley systems and the like. It should be understood that various actuator systems which deploys and retract the cable will be usable with the present invention.

Referring to FIG. 2C, the actuator system 54 engages an end segment 58A of the cable 58 such that the cable 58 may be spooled and unspooled to increase or decrease the length thereof. The cable 58 is wound around a spool 66 at one end segment 58A while the other end segment 58B is attached to a fixed attachment such as one of the fixed structure 34R. By spooling the cable 58 around the spool 66, the effective circumferential length of the cable 58 is effectively decreased (shown in phantom) such that the fan nozzle exit area 44 is decreased. By unspooling the cable 58 from the spool 66, the effective circumferential length of the cable 58 is effectively increased (shown solid) such that the fan nozzle exit area 44 is increased. The bypass flow B permits unilateral operation of the FVAN such that the bypass flow B diverges the flaps 50 and the FVAN 42 need only be driven (cable 58 retracted) to overcome the bypass flow B pressure which results in a significant weight savings. This advantage of the present invention allows practical use of the variable area nozzle on the gas turbine engines.

Whereas the diverged shape is utilized for landing and takeoff flight conditions, should the cable 58 break, the FVAN 42 will failsafe to the diverged shape. It should be understood, however, that positive return mechanisms may alternatively or additionally be utilized.

Each cable 58 preferably pitches one flap set between the converged position (shown in phantom) and a diverged position. It should be understood that although four sectors are illustrated (FIG. 1C), any number of sectors may alternatively or additionally be provided. It should be further understood that any number of flaps 50 may be controlled by a single cable 58 such that, for example only, the single cable may be strung around the entire circumference of the fan nacelle 34, however, a sector arrangement is preferred to provide asymmetric capability to the FVAN 42.

The foregoing description is exemplary rather than defined by the limitations within. Many modifications and variations of the present invention are possible in light of the above teachings. The preferred embodiments of this invention have been disclosed, however, one of ordinary skill in the art would recognize that certain modifications would come within the scope of this invention. It is, therefore, to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described. For that reason the following claims should be studied to determine the true scope and content of this invention. 

What is claimed is:
 1. A method of providing a variable fan exit area of a high-bypass gas turbine engine comprising the steps of: (A) locating a fan variable area nozzle to define a fan nozzle exit area for flow passing between a fan nacelle and a core nacelle; (B) stringing a cable to pass through a fan nacelle first fixed engagement structure, then through a flap extension opening and then through a fan nacelle second fixed engagement structure wherein the flap extension opening is located between the first fixed engagement structure and the second fixed engagement structure; (C) locating said flap extension opening in a flap extension protruding from a leading edge of a flap, said flap extension opening upstream of a flap pivot point, said fan nacelle first fixed engagement structure and said fan nacelle second fixed engagement substantially aligned with lateral sides of said flap and at least one of said first and second fixed engagement structures having a cable opening located upstream of said flap pivot point; (D) providing an actuator system that includes a spool engaged with said cable, a segment of said cable opposite said actuator system being attached to a fixed structure within said fan nacelle; (E) spooling and unspooling the cable engaged with said fan variable area nozzle to vary the fan nozzle exit area by pivoting a plurality of said flaps to adjust fan bypass airflow such that an angle of attack of turbofan fan blades are maintained close to design incidence; and (F) wherein unspooling said cable extends the cable to enable said flow to urge a trailing edge of at least one of said plurality of said flaps outwardly and increase said area.
 2. A method as recited in claim 1, wherein said step (B) further comprises: (a) spooling the cable to converge the fan nozzle exit area during cruise flight condition.
 3. A method as recited in claim 1, wherein said step (B) further comprises: (a) stringing one end of the cable about the spool and the opposite end of the cable to the fixed structure with said plurality of said flaps strung therebetween.
 4. A method as recited in claim 1, wherein the actuator system comprises a rotary hydraulic actuator.
 5. A nacelle assembly for a gas turbine engine comprising: a core nacelle defined about an axis for allowing flow to pass therethrough; a fan nacelle mounted at least partially around said core nacelle, said fan nacelle having a plurality of lateral ribs and a fan variable area nozzle that defines a fan exit area between said fan nacelle and said core nacelle, said nozzle having a plurality of flaps that pivot about a pivot, each flap associated with a pair of said lateral ribs, at least one of the pair of lateral ribs having a rib orifice located upstream of a leading edge of said each flap, said each flap having an extension protruding from said leading edge upstream of said pivot and between said pair of lateral ribs; a cable engaged with said fan variable area nozzle within said fan nacelle, said cable routed from the rib orifice in one of said pair of lateral ribs, said cable then routed through an orifice in said extension, said cable then routed to the other of said pair of lateral ribs; and, an actuator system that mechanically retracts said cable therein pivoting a trailing edge of said flaps about said pivot inwardly to lessen said fan exit area and mechanically extends said cable to enable said flow to pivot said trailing edge of said flaps about said pivot outwardly and increase said fan exit area, wherein said actuator system is engaged with said cable, and a segment of said cable, opposite said actuator system, is attached to a fixed structure within said fan nacelle.
 6. The nacelle assembly as recited in claim 5, wherein said actuator system includes a spool configured to spool and unspool said cable.
 7. The nacelle assembly as recited in claim 5, wherein said actuator system includes a spool engaged with said cable.
 8. The nacelle assembly of claim 7, wherein spooling of the cable around the spool decreases the fan nozzle exit area.
 9. The nacelle assembly of claim 7, wherein unspooling of the cable around the spool increases the fan nozzle exit area.
 10. The nacelle assembly as recited in claim 5, wherein said fan variable area nozzle includes a multiple of flap sets, each of said flap sets separately driven by a respective cable and actuator of said actuator system to asymmetrically and symmetrically adjust said fan variable area nozzle.
 11. The nacelle assembly of claim 10, wherein each flap set corresponds to a circumferential sector of the fan variable area nozzle.
 12. The nacelle assembly of claim 11, wherein there are four circumferential sectors.
 13. The nacelle assembly as recited in claim 5, further comprising: a gear system driven by a core engine; and a fan driven by said gear system about said axis.
 14. The nacelle assembly of claim 5, wherein the actuator system comprises one of an electromechanical actuator or a rotary hydraulic actuator.
 15. The nacelle assembly for a gas turbine engine of claim 5 wherein there is one actuator system for a set of flaps.
 16. The nacelle assembly of claim 5, wherein the actuator system comprises a rotary hydraulic actuator.
 17. The nacelle assembly of claim 5, wherein the cable circumscribes the fan nacelle.
 18. The nacelle assembly of claim 5, wherein the fixed structure is a fan nacelle rib.
 19. An assembly for pivoting a plurality of flaps, said assembly disposed about an axis along which a flow passes from an upstream direction to a downstream direction, said assembly comprising: a structure mounted at least partially around said axis, said structure having plurality of lateral ribs, said structure having a plurality of pivots attaching thereto, each pivot attaching to a flap wherein said plurality of flaps define a nozzle area and wherein each flap pivots about said pivot, each flap associated with a pair of said lateral ribs, at least one of the pair of lateral ribs having a rib orifice located upstream of a leading edge of said each flap, said each flap having an extension protruding from said leading edge upstream of said pivot and between said pair of lateral ribs; a cable engaged with said nozzle within said structure, said cable routed from the rib orifice in one of said pair of lateral ribs, said cable then routed through an orifice in said extension, said cable then routed to the other of said pair of lateral ribs; and an actuator system that mechanically retracts said cable therein to lessen the nozzle area and mechanically extends said cable to enable said flow to urge said flaps outwardly and increase said area, wherein: said actuator system engaged with said cable, and a segment of said cable, opposite said actuator system, is attached to a fixed structure within said fan nacelle. 